In the Bristol University study, led by Professor Debbie Lawlor of its School of Social and Community Medicine, more than 5,000 children aged nine to 12 were measured for body mass index (BMI) and other indicators of fatness.

They were measured again at 15, when their blood pressure was also taken and blood samples analysed.

At the younger age almost a quarter were either overweight or obese (18.5 per cent and 4.5 per cent respectively). Those who remained so at 15 had significantly higher blood pressure, cholesterol and insulin levels than thinner children.

However, those who thinned-down tended to reduce their risk factors, with girls appearing to recover better than boys.